The invention relates to ceramic foam for filters for cleaning exhaust gases of diesel engines.
In certain operating conditions of diesel engines, it has turned out that ceramic foam diesel soot filters which filter efficiently per se, have a zero or only very low degree of particle filtration. This happens particularly at high exhaust temperatures and exhaust velocities, that is, above all when the diesel engines are running under full load. The inadequate degree of particle filtration is traced back to excessively low adhesion of soot particles to the ceramic foam. An inadequate coefficient of adhesion limits the probability of soot retention within the ceramic foam, and therefore soot agglomerates can no longer form. But the latter are necessary for obtaining the deep-action efficiency of filters of this kind.
In view of the circumstances, the inventors set themselves the aim of increasing the filter action in a diesel soot filter with ceramic foam by increasing the adhesion of soot particles, in such a way that the filter has a high degree of filtration in all operating conditions of the diesel engine, particularly also in the range in which so-called dry soot accumulates, that is, soot which is free from adsorbed hydrocarbons.
It is therefore the object to prepare a ceramic foam filter which attains the aim, and specify a method for the manufacture of a ceramic foam filter of this kind.
Hydrocarbons usually promote the adhesion of soot inside the porous ceramic foam structure. Thus, when hydrocarbons are absent from the exhaust gases or their content is below average, the rate of filtration of soot particles is reduced as well, if ordinary ceramic foam is used.